Sheet with improved image durability

ABSTRACT

Pressure sensitive recording sheets of improved image durability are obtained due to the pressure of a hydrogen quinoline compound.

[451 Sept. 3, 1974 1 1 SHEET WITH IMPROVED IMAGE DURABILITY [75] Inventors: Hiroharu Matsukawa; Takao Hayashi, both of Shizuoka, Japan [73] Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan [22] Filed: Nov. 12, 1971 [21] Appl. No.: 198,316

[30] Foreign Application Priority Data Nov. 13, 1970 Japan 45-99983 [52] US. Cl 1l7/36.2, 106/22, 117/36.8, 117/36.9, 260/283 R, 260/288 R, 260/289 R [51] Int. Cl. B41c 1/06 [58] Field of Search 117/36.2, 36.8, 36.9; 260/283 R, 288 R, 289 R; 106 /22 [56] References Cited UNITED STATES PATENTS 3,121,650 2/1964 Meissner ll7/36.2 X

0-6 C 75 0 5 E o 0-4 3,293,061 12/1966 1 lWlOll 177/36 8 3,501,331 3/1970 Kimuru et al. 117/36 2 3,514,310 5/1970 Kimura et a1. 117/36 2 3,565,666 2/1971 Phillips 117/36 2 3,642,514 2/1972 Orita et al.. 177/36 2 3,669,711 6/1972 Kimura eta 117/36 2 FOREIGN PATENTS OR APPLICATIONS 15,204 7/1908 Great Britain 117/36.2 203,329 9/1956 Australia ll7/36.2

Primary Examiner-William D. Martin Assistant ExaminerM. R. Lusignan Attorney, Agent, or Fir'mRichard C. Sughrue [57] ABSTRACT Pressure sensitive recording sheets of improved image durability are obtained due to the pressure of a hydrogen quinoline compound.

10 Claims, 4 Drawing Figures 400 150 500 '550 600 1350' ioo WAVELENGTH (mp) PATENIED Hum!) FIGNI) ioo 400 550 500 '550 @500 'sso oo WAVELENGTH (mp) WAVELENGTH (mp) WAVELENGTH (mp) WAVELENGTH (mp) SHEET WITH IMPROVED IMAGE DURABILITY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an organic oily color former composition for pressure-sensitive recording. More particularly, it is concerned with a method whereby the durability of a developed color material is increased, and discoloration is inhibited, said developed color matter being formed by the contact reaction of a leuco dye (which will hereinafter be referred to as a color former) with a developer in the presence of a hydrogen quinoline derivative.

2. Description of the Prior Art The contact reaction between a color former and developer for recording or copying sheet use are known. For example, one system comprises a solution of a color former dissolved in an organic solvent which is transferred to a developer sheet to obtain a developed color image.

A further system comprises a capsule sheet and a developer sheet which are combined so as to face the capsule surface and the developer surface. The capsule sheet is prepared by enclosing fine drops of a solution of color former dissolved in an organic solvent in capsules and applying them to a support member. Total pressure breaks the capsules and the color former solution is transferred to the developer surface to thus obtain a developed color image.

The no carbon system is of the latter type, but here the microcapsule components and the developer components are coated onto the same support member.

Examples of color formers used in the foregoing recording or copying systems are triarylmethane type compounds, diphenylmethane type compounds, xanthene type compounds, thiazine type compounds and spiropyran type compounds.

Examples of developers used in such systems are clays such as acidic clays, active clays, attapulgite, zeolite and bentonite, organic acids such as tannic acid, gallic acid and pentachlorophenol, and phenolic resins.

The durability to light of developed color matter formed by the contact reaction of the above mentioned color formers and developers is much lower that of pigments, and developed color matter formed from some color formers tends to discolor under the influence of light.

Various developed color materials differ in durability and discolor or fade to various extents, so that the color tone of a developed blue, blue-black, green or black image. above all a developed black image, may deteriorate and show poor durability.

Developed color materials formed from the only practical color former used for forming developed blue, blue-black or green images, that is, thiazine type compounds, are not suitable for the production of a practical recording sheet because the density thereof lowers and the original color tone varies when they are allowed to stand in a room or exposed to sunlight.

In order to obtain a developed blue image a combination of crystal violet lactone and benzoyl leuco methylene blue is generally used as the color former. However, even if a blue image is temporarily formed by the contact of this combination with a developer, the color image vanishes when allowed to stand in a room or ex- For developed red color the fluoran compounds I mentioned in BP 1,168,455 are often used. However, the durability of such developed color materials is lower than that of the thiazine compounds.

SUMMARY OF THE INVENTION One object of the invention is to raise the durability of a developed color material formed by the contact reaction of a color former and a developer.

It is another object of the invention to minimize the color change of a developed color material formed by the contact reaction of a color former and a developer.

It is a further object of the invention to raise the durability of a recorded image or a copied image formed by recording or copying utilizing the contact reaction of a color former and developer as well as to prevent the color change thereof, thus resulting in improving its commerical value.

We the inventors have accomplished the above mentioned objects by the use of a combination of a color former and a hydrogen quinoline derivative.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 4 are spectral absorption curves comparing the present invention to various prior art systems.

DETAILED DESCRIPTION OF THE INVENTION A color former is reacted with an acid in the presence of an oxidizing agent, which is usually air, to form a distinct color. Accordingly, the color former mustbe prevented from contacting the acid and oxidizing agent before use as a recording sheet. However, the color former before use is generally influenced to a certain extent by acid and oxygen in the atmosphere to form a color.

The hydrogen quinoline derivatives of the present invention are effective in preventing the color former from oxidation. The reason why the derivatives are effective has not been definitely determined, but it is believed that hydrogenated quinoline nuclei represented by the following formulae,

gives the oxidation-preventing action on the color former.

The hydrogen quinoline derivatives of the greatest use are represented by the following formula: wherein R is hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a phenyl group, R is hydrogen, an alkoxyl group having 1 to 2 carbon atoms, an alkyl 'dihydroquinoline,

group having l to 4 carbon atoms, an alkylamine having 1 to 4 carbon atoms, a dialkylamine having l to 4 carbon atoms, benzylamine, dibenzylamine or an amino group, and R is hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

The hydrogen quinoline derivatives may be prepared by any known method. For example, the derivative may be obtained by the reaction of aniline or a derivative thereof with an aliphatic aldehyde or ketone in the presence of a catalyst such as hydrogen chloride, sulfuric acid, iodine, bromine or aromatic sulfonic acid. In the case of preparing an alkyl hydrogen quinoline, the alkyl hydrogen quinoline is simultaneously often polymerized to provide a polymer of the derivative having various polymerization degrees. Therefore, polymers of the derivative can also be effectively used in the invention.

The most prefered derivatives of hydrogen quinoline are represented by the formula,

R R: l

f R R1 wherein R, R and R are same as the above definition.

Derivatives having a substituent in the 6-position thereof are very effective. Further, the higher the electron positive degree of the substituent R the more effective is the substituent.

Illustrative of the hydrogen quinoline derivative used in the present invention are l,2-dihydroquinoline, 2,2,- 4-trimethyldihydroquinoline, l,2,3,4- tetrahydroquinoline, 6-methyldihydroquinoline, 6,6- methylene-bis-trihydroquinoline, I-methyl-Z-phenyl- 1,2-dihydroquinoline, 1,2,2-trimethyll ,2- dihydroquinoline, 6-amino-2,2,4-trimethyl-l,2 -dihydroquinoline, 6-diethylamino-2,2,4-trimethyl-1,2- dihydroquinoline, 6-ethylamino-2,2,4-trimethyl-l,2- 6-ethoxy-2,2,4-trimethyl-1,2- dihydroquinoline, etc. These hydrogen quinoline derivatives may be used alone or in mixture in an amount of l-5007c, preferably 50-2007c, based on the color former used.

Most preferably, the amount of hydrogen quinoline derivative is less than 20 wt.% of the solvent and for general use the color former will be 2 wt.% to 20 wt.% of the solvent. However, it will be clear from the 10-500 wt.% hydrogen quinoline derivative: color former range, the above proportions to solvent can be varied gently.

When the instant invention is practised with a colorless color former ink, the hydrogen quinoline derivative may be directly dissolved in an organic solvent in which the color former is dissolved. Contact of this ink with a developer sheet results in a developed color matter excellent in durability.

ln the case of application to a pressure-sensitive recording paper, the hydrogen quinoline derivative of the invention is dissolved in an organic solvent in which a color former is already dissolved and the resulting solution is microencapsulated followed by coating onto a support.

In a further embodiment of the invention, moreover, an organic solvent solution of the hydrogen quinoline derivative of the invention is encapsulated, mixed with another encapsulated organic solvent solution of a color former and applied to a support.

When the capsules on the above mentioned capsule sheet are broken and the color former and developer are brought into contact with each other, a developed color matter excellent in durability is obtained.

As is apparent from the foregoing, the main feature of the present invention is to raise the durability of a developed color matter formed by the contact reaction of a color former and developer by the action of a hydrogen quinoline derivative.

It will be readily understood, therefore, that, in the case of applying the invention to a color ink, any wellknown solvent may be used, and in the case of a pressure-sensitive recording paper there are no restrictions on the solvent, capsule forming method, developer, coating methods or form of the sheet.

Representative of the many solvents which can be used are one or more of the natural or synthetic oils, for example, chlorinated biphenyls, chlorinated terphenyls, alkylated biphenyls, alkylated terphenyls, chlorinated paraffins, chlorinated naphthalenes, alkylated naphthalenes, kerosene, paraffin, naphthene oils and cotton seed oil.

Typical of the capsule formation methods are those utilizing the coacervation of a hydrophilic colloid sol as described in U.S. Pat. No. 2,800,457, 2,800,458, and typical of those utilizing interfacial polymerization are those described in BP 867,797, 950,443, 989,264 and 1,091,076. I

The color developing materials of the prior art are used as a developer capable of forming a developed color matter in contact with the color former.

Coating may be carried out by any coating system, such as, air knife coating, blade coating, roll coating or by any known printing system.

in the practice of the invention the color former is not particularly limited but examples thereof are: triarylmethane type compounds such as 3,3-bis(pdimethylaminophenyl)-6-dimethylaminophthalide, i.e., crystal violet lactone (which will hereinafter be referred to as CVL), 3,3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-( 1,2-

dimethylindole-3-yl)phthalide, 3-( pdimethylaminophenyl)-3-( 2-methylindole-3-yl)phthalide, 3-(pdimethylaminophenyl )-3-( 2- phenylindole-3-yl )phthalide, 3,3-bis( l,2- dimethylindole-3-yl)-5-dimethylaminophthalide, 3,3-

bis( l,2-dimethylindole-3-yl)-6- dimethylaminophthalide, 3,3-bis(9-ethylcarbazole-3- yl )-5-dimethylaminophthalide, 3,3bis(2-phenylindole- 3-yl)-5-dimethyl-aminophthalide and 3-pdimethylaminophenyl-3-( l-methylpyrrole-2-yl)-6- dimethylaminophthalide, diphenylmethane type compounds such as 4,4-bis-dimethylaminobenzhydrinbenzyl ether, N-halophenyl-leuco auramine and N245- trichlorophenyl leuco auramine, xanthen type compounds such as rhodamine B-anilinolactam, rhodamine Bp-nitroanilinolactam, rhodamine B-pchloroanilinolactam, 7-dimethylamino- 2-methoxyfluoran, 7-diethylamino-2-methoxyfluoran, 7-diethylamino-3-methoxyfluoran, '7-diethyl-amino-3- chlorofluoran, 7-diethylamino-3-chloro-2- methylfluoran, 7-diethylamino-2,3-dimethylfluoran, 7-diethylamino-3-acetylmethylaminofluoran, 7-

diethylamino-3'-methylaminofluoran, 3,7- diethylaminofluoran, 7-diethylamino 3- dibenzylaminofluoran, 7-diethylamino-3-methylbcnzylaminofluoran, 7-diethylamino-3-chloroethylmethylaminofluran and 7-diethylamino-3- diethylaminofluoran, thiazine type compounds such as benzoyl leuco methylene blue and p-nitrobenzyl leuco methylene blue, spiro compounds such as 3-methylspiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3,3'-dichloro-spiro-dinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho-(3-methoxybenzo)-spiro-pyran and 3-propyl-spiro-dibenzopyran.

The following examples are given in order to illustrate the invention in more detail without limiting it, in which a developer sheet used for assessment of the effect whether the durability of a developed color matter is raised is prepared by the following procedures: 100 parts of a sulfuric acid-treated acid clay (sulfuric acid treatment is carried out by immersing the acid clay into sulfuric acid, whereby the surface area of the acid clay is increased is dispersed in 280 parts of water containing 6 parts of a 40% caustic soda solution by a homogenizer) to which 50 parts of a aqueous solution of the sodium salt of casein and 30 parts of a styrenebutadiene latex (Trade Mark: Dowlatex 626, made by Dow Chemical Co.) are then added, and the resulting dispersion is applied to an original paper of 50 g/m to give a coating of lOg/m by air knife coating, followed by drying. Enough samples of this developer sheet were made to be used in all of the following examples.

Example 1 In a mixed oil consisting of 40 parts of chlorinated biphenyl (degree of chlorination: 30 wt.%; when present the same chlorinated biphenyl was used in the following examples) and 10 parts of kerosene were dissolved 1 part of crystal violet lactone as a color former and then 1 part of a polymer of 2,2,4-trimethyI-l,2- dihydroquinoline as a dihydroquinoline derivative (Trade Mark: Antigen RD, made by Sumitomo Chemical Industry Co.) was added thereto, thus obtaining a color former oil. The oil was added to an aqueous solution consisting of 10 parts of gum arabic and 60 parts of warm water at 40C to form an oil-in-water type emulsion having a drop size of 6-10 microns. 10 parts of an acid-treated gelatin having an isoelectric point of 7.8 was dissolved in 80 parts of warm water at 40C and added thereto. With constant agitation 50% acetic acid was added thereto to adjust the pH to 4.2. 250 parts of warm water at 40C was further added to cause coacervation. During the same time, a thickened liquid film of gelatin and gum arabic was formed round the oil drop. The internal temperature was lowered to 10C to gel the thus formed thickened liquid film and 4 parts of 37% formaldehyde was added to harden the wall film. After adding 40 parts of a 10% aqueous solution of carboxymethyl cellulose, a 10% aqueous castic soda solution was dropwise added to raise the pH to 9.5 and the liquid temperature was raised to 50C, thereby increasing the effect of hardening.

The resulting capsules were applied to an original paper of 40 g/m by air knife coating to give a coating of 6.0 g/m followed by drying and a capsule sheet was obtained. a

Example 2 Example I was repeated using 1 part of 3-methyl- 2,2'-spirobi(benzo(f)chromene) in place of 1 part of crystal violet lactone as a color former. 4

The resulting capsules were applied to an original paper of 40g/m by air knife coating to give a coating of 6.0 g/m followed by drying and a capsule sheet was obtained.

Example 3 Example I was repeated using 1.5 parts of 3-N,N- dimethylamino-6,8-dimethylfluoran in place of 1, part of crystal violet lactone as a color former.

The resulting capsules were applied to an original paper of 40 g/m to give a coating of 6.0 g/m by air knife coating, followed by drying and a capsule sheet was obtained.

Example 4 Example I was repeated using 2.4 parts of 3-N,N- diethylamino-7-(N,N-diethylamino)fluoran in place of 1 part of crystal violet lactone as a color former.

The resulting capsules were applied to an original paper of 40 g/m by air knife coating to give a coating of 6.0 g/m followed by drying and a capsule sheet was obtained.

Comparative Examples But for adding no Antigen RD as a hydrogen quinoline derivative, capsules of Comparative Examples 1, 2, 3 and 4 were prepared exactly as in corresponding Examples 1 to 4, respectively. The capsules were applied to an original paper of 40 g/m so as to give a coating of 6.0 g/m followed by drying and capsule sheets of Comparative Examples 1 to 4 were obtained.

Comparative Test Result 1 Capsule sheets of Examples 1 to 4 and Comparative Examples 1 to 4 each was stacked on a developer sheet and color formed under a pressure of 600 kg/cm After standing in the dark for 1 hour, the spectral absorption curve (A) of a developed color matter was measured between wavelengths of 700 a to 400 ,u. Further measurements were made after radiation by sunlight for 1 hour (B) and for 3 hours (C). The results are shown in FIG. 1 to FIG. 4.

In FIG. 1, [I] shows Example I and [II] shows Comparative Example 1. In FIG. 2. [I] show Example 2 and [II]. Comparative Example 2. In FIG. 3, [I] shows Example 3 and [II] Comparative Example 3. In FIG. 4, [I] shows Example 4 and [II] Comparative Example 4. Measurement of the spectral absorption curve was carried out by the use of Beckmann DB type spectrophotometer.

The value of light resistance is obtained by the fol lowing relation and shown in Table 1.

Light resistance (A/B) X A: Density at the absorption maximum after exposure to the sunlight B: Fresh density at the absorption maximum The larger this value is, the better durability of a developed color material.

Table l Light resistance at the absorption maximum after exposure to sunlight Table l-Continued Light resistance at the absorption maximum after exposure to sunlight Radiation of Radiation of Wavelength sunlight sunlight measured 1 hour 3 hours Comparative Example 2 74.2 7r 38.8 7( 625 mp.

Example 3 98.l 7: 82.1 71 500 mu Comparative Example 3 89.8 7r 75.8 7r 500 mu Example 4 (A 94.6 71 77.3 7: 437 mp. do. (A 87.8 60.9 A 600 mu Comparative Example 4 (M) 81.2 71 57.7 437 mp. 600 do (A 57 7 "/1 28.8 "/1 "V The shift of A due to exposure to sunlight is tabulated below from the spectral absorption curves of Example 4 and Comparative Example 4.

TABLE 2 Shift of the absorption maximum due to exposure to sunlight of 3-N.N-diethylamino-7-N.N-diethylaminofluoran Fresh After exposure After exposure (my) to sunlight to sunlight 1 hour (mu) 3 hours (mu) Example 4 605 598 560 Comparative Example 4 605 550 510 chlorinated biphenyl (oil) 40 parts chlorinated paraflin with a chlorination degree 30 (oil) 5 parts normal paraffin (diluted oil) 5 parts 3-N.N-dieth vlamino-7-N.N-dibenzylaminofluoran (color former) 2.5 parts 6-ethoxy-2 2.4-trimethyl- I .2-dihydroquinoline (hydrogen quinoline derivative) 2.0 parts The foregoing color former oil was encapsulated according to the procedure of Example 1. The resulting microcapsules were applied to an original paper of 40 g/m by air knife coating to give a coating of 6.0 g/m followed by drying and a capsule sheet was obtained.

On the other hand, a color former oil having the same recipe as mentioned above but omitting 6-ethoxy- 2,2,4-trimethyl-l,Z-dihydroquinoline as a hydrogen quinoline derivative was prepared, encapsulated according to Example 1 and applied to an original paper of 40 g/m by air knife coating to give a coating of 6.0 g/m followes by drying, and a capsule sheet of Comparative Example 5 was obtained.

Comparative Test Result 2 Capsule sheets of Example 5 and Comparative Example 5 each was stacked on a developer sheet, color formed under a load pressure of 600 kg/cm and the light resistance and wavelength shift were measured according to Comparative Test 1 to obtain results as shown in Tables 3 and 4.

TABLE 3 Light resistance at absorption maximum M,

(440 mu) and A. ,(6l0 mp.) when 3-N,N-diethylamino-7-N,Ndibenzylaminofluoran is irradiated with sunlight Radiation Radiation of sunlight of sunlight 1 hour 3 hours Example 5 (M) 90.5 72 758 7r (A 85.6% 61.4%

Comparative Example 5 (M) 80.4 55.3 75 (A!) 54.3 25.6

TABLE 4 Shift of absorption maximum Dk (6l0 mu) by irradiation with sunlight of 3-N,N-diethylamino-7-N.N-dihenzylaminofluoran A A: after after of fresh irradiation irradiation (mu) with sunlight with sunlight for l hour for 3 hours i -l (my) Example 5 6l0 585 560 Comparative Example 5 610 560 520 Example 6 The following were mixed and dissolved as a color former oil: 1

dimethylnaphthalene (oil) 30 parts normal paraffin (diluted oil) 20 parts 7-diethylamino-Z.3-dimethylfluoran (color former) 2.0 parts 6-ethylamino-2,2.4-trimethyl- LZ-dihydroquinoline (hydrogen quinoline derivative) 1.5 parts The thus obtained color former oil was encapsulated according to the precedure of Example 1, applied to an original paper of 40 g/m by air knife coating to give a coating of 6.0 g/m followed by drying, and a capsule sheet was obtained.

On the other hand, a color former oil having the same recipe as mentioned above but omitting 6-ethylamino- 2,2,4-trimethyll ,Z-dihydroquinoline was prepared, encapsulated according to Example 1, applied to an original paper of 40 g/m by air knife coating to give a coating of 6.0 g/m dried and a capsule sheet of Comparative Example 6 was thus obtained.

Comparative Test Result 3 Capsule sheets of Example 6 and Comparative Example 6 each was stacked on a developer sheet, color formed under a load pressure of 600 kg/cm and the light resistance was measured according to Comparative Test 1 to obtain results as shown in Table 5.

TABLE Light resistance at absorption maximum A, (535 mp.) when 7-diethylamino-Z,3-dimethylfluoran is-irradiated with sunlight Radiation Radiation of sunlight of sunlight 1 hour 3 hours Example 6 96.3 7L 81.5 /1- Comparative Example 6 87.4 70.5

Example 7 The following were prepared for a color former oil:

chlorinated hiphenyl (oil) 45 parts isoparall'in (diluted oil) 5 parts crystal violet laetone (color former) l part benzoyl leuco methylene blue (color former) 0.5 part 3-methyl 2.2'-spirobis (henzo (flehromene) (color former) 1 part 2,2,-1triinethyl-dihydroquinoline (hydrogen quinoline derivative) l part When this color former oil was directly transferred to a developer sheet by the printing system, a developed blue image was obtained.

On the other hand, a color former oil having the same recipe as mentioned above but omitting 2,2,4-trimethyldihydroquinoline was prepared and similarly transferred to a developer sheet by a printing system, thus obtaining a developed blue image (Comparative Example 7). The values of light resistance of these developed color image are shown in Table 6 (measured wavelength: 610 a).

TABLE 6 Light resistance of developed hlue image Radiation Radiation of sunlight of sunlight 1 hour 3 hours Example 7 90 "/r 83 7! 11' all Example 85 '71 757! Example 8 The following were prepared for a color former oil:

tlielhyl terphenyl (oil) 45 parts normal paral'l'in (diluted oil) 5 parts 1-( N-dichloroethyl )aniinwodietliylaminolluoran (color former) 4 parts -Continued benzoyl leuco methylene blue (color former) l parts 6-ethylamino2,2,4-triethyll,2-dihydroquinoline (hydrogen quinoline derivative) I 2 parts When this color former oil was directly transferred to a developer sheet by a printing system, a developed green image was obtained.

On the other hand, a color former oil having the same recipe as mentioned above but omitting 6-ethylamino- 2,2,4-trie'thyl-1,2-dihydroquinoline was prepared and similarly transferred to a developer sheet by a printing system, thus obtaining a developed green image (Comparative Example 8). The values of light resistance of these developed color image are shown in Table 7 (measured wavelength 600 mu).

TABLE 7 Light resistance of developed green image Radiation Radiation of sunlight of sunlight 1 hour 3 hours Example 8 95 A 88 "/1 Comparative Example 8 85 '71 "/1 the formula:

I R R1 wherein R is hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a phenyl group, R is hydrogen, an alkoxyl group having 1 to 2 carbon atoms, an alkyl group having 1 to 4 carbon atoms, an alkylamine having 1 to 4 carbon atoms, a dialkylamine having 1 to 4 carbon atoms, benzylamine, dibenzylamine or .an amino group, and R isihydrogen atom or an alkyl group having 1 to 4 carbon atoms; and

R in 1:

1t \N/ R wherein R is hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a phenyl'group R is hydrogen, an alkoxyl group having l to 2 carbon atoms, an alkyl group having 1 to 4 carbon atoms, an alkylamine having 1 to 4 carbon atoms, a dialkylamine having 1' to 4 carbon atoms, benzylamine, dibenzylamine or an amino group, and R is hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

4. The pressure-sensitive recording sheet of claim 1 wherein said electron donating colorless organic compound as a color former is selected from the group consisting of triarylmethane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds and spriopyran compounds 5. The pressure-sensitive recording sheet of claim 1 wherein said hydrogen quinoline compound increases the durability to light and inhibits the discoloration of the reaction product of the color former and color developer without itself yielding a colored reaction product.

6. The pressure-sensitive recording sheet of claim 1 7. The pressure-sensitive recording sheet of claim I wherein said hydrogen quinoline compound is of the formula wherein R is hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a phenyl group, R is hydrogen, an alkoxyl group having 1 to 2 carbon atoms, an alkyl group having 1 to 4 carbon atoms, an alkylamine having 1 to 4 carbon atoms, a dialkylamine having 1 to 4 carbon atom, benzyl amine, dibenzylamine or an amino group, and R is hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

8. The pressure-sensitive recording sheet of claim 1 wherein said hydrogen quinoline compound is of the formula;

R R2 I \IYI R wherein R is hydrogen atom, analkyl group having 1 to 4 carbon atoms or a phenyl group, R is hydrogen, an alkoxyl group having 1 to 2 carbon atoms, an alkyl 1 group having 1 to 4 carbon atoms, an alkylamine havwherein the hydrogen quinoline compound is present in an amount of 10 to 500%, based on the color former.

ing 1 to 4 carbon atoms, a dialkylamine having 1 to 4 carbon atoms, ben zyl amine, dibenzylamine or an amino group, and R is hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

9. The pressure-sensitive recording sheet of claim 6 wherein the amount of hydrogen quinoline compound is less than 20 wt. of the organic solvent.

10. The pressure-sensitive recording sheet of claim 9 wherein the color former is from 2 wt. to 20 wt.

of the solvent. 

2. The pressure-sensitive recording sheet of claim 1 wherein said hydrogen quinoline compound is selected from the group consisting of 1,2-dihydroquinoline, 2,2,4-trimethyldihydroquinoline, 1,2,3,4,-tetrahydroquinoline, 6-methyldihydroquinoline, 6,6-methylene-bis-trihydroquinoline, 1-methyl-2-phenyl-1,2-dihydroquinoline, 1,2,2-trimethyl-1,2-dihydroquinoline, 6-amino-2,2,4-trimethyl-1,2-dihydroquinoline, 6-diethylamino-2,2,4-trimethyl-1,2-dihydroquinoline, 6-ethylamino-2,2,4-trimethyl-1,2-dihydroquinoline and 6-ethoxy-2,2, 4-trimethyl-1,2-dihydroquinoline.
 3. The pressure-sensitive recording sheet of claim 1 wherein the organic solvent is a natural or synthetic oil.
 4. The pressure-sensitive recording sheet of claim 1 wherein said electron donating colorless organic compound as a color former is selected from the group consisting of triarylmethane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds and spriopyran compounds.
 5. The pressure-sensitive recording sheet of claim 1 wherein said hydrogen quinoline compound increaseS the durability to light and inhibits the discoloration of the reaction product of the color former and color developer without itself yielding a colored reaction product.
 6. The pressure-sensitive recording sheet of claim 1 wherein the hydrogen quinoline compound is present in an amount of 10 to 500%, based on the color former.
 7. The pressure-sensitive recording sheet of claim 1 wherein said hydrogen quinoline compound is of the formula
 8. The pressure-sensitive recording sheet of claim 1 wherein said hydrogen quinoline compound is of the formula;
 9. The pressure-sensitive recording sheet of claim 6 wherein the amount of hydrogen quinoline compound is less than 20 wt. % of the organic solvent.
 10. The pressure-sensitive recording sheet of claim 9 wherein the color former is from 2 wt. % to 20 wt. % of the solvent. 